Digger tooth

ABSTRACT

A digger tooth having a cutting portion the lateral crosssection of which is defined by two curved surfaces, these being forming the upper and lower tooth surfaces, and varying in profile such that the thickness of the lateral section of the tooth varies from the center of the tooth outwardly at approximately a ratio of 1:4. Thus, since the edges of the tooth are thicker and therefore stronger, wear tends to take place in such a manner that the primary cutting portions of the tooth, defined by the edges, precede the excavating portion by a distance dependent upon the angle of attack of the tooth into the formation being dug.

United States Patent White June 10, 1975 1 1 BIGGER TOOTH 3,326,3026/1967 Washbond et a1. 172/713 3,396,671 8/1968 Roseber 172/771 x [75]Inventor: Kenneth Calgary 3,534,818 10/1970 Mascaro 172/540 x Albefla-Canada 3,624,827 11/1971 Liess.......... 37/142 R [731 Assign: 9?"Company FOREIGN PATENTS OR APPLICATIONS Calgary Alberta Canada 421,8991/1935 United Kingdom 37/142 R 22 Filed: Sept. 10, 1974 455,459 3/1949Canada .1 172/372 1,139,312 1/1969 United Kingdom 172/713 App]. No.:504,697

Related U.S. Application Data Continuation of Ser. No. 373,939, June 27,1973, abandoned.

[30] Foreign Application Priority Data May 29, 1973 Canada 172630 [52]US. Cl 37/142 R; 172/713; 299/79 [51] Int. Cl E02i 9/28 [58] Field ofSearch 37/141 R. 142 R. 142 A. 37/189,191 A; 172/713, 719, 765, 699,604, 540; 294/54, 55; 299/79, 88, 91-93 [56] References Cited UNITEDSTATES PATENTS 1,395,048 10/1921 McKee 37/142 R 3,103,752 9/1963Rockwell 172/771 X Primary ExaminerE. H. Eickholt ABSTRACT A diggertooth having a cutting portion the lateral cross-section of which isdefined by two curved surfaces, these being forming the upper and lowertooth surfaces, and varying in profile such that the thickness of thelateral section of the tooth varies from the center of the toothoutwardly at approximately a ratio of 1:4. Thus, since the edges of thetooth are thicker and therefore stronger, wear tends to take place insuch a manner that the primary cutting portions of the tooth, defined bythe edges, precede the excavating portion by a distance dependent uponthe angle of attack of the tooth into the formation being dug.

7 Claims, 9 Drawing Figures PATENTEDJUN 10 1975 3 888 28 SHEET 2PATENTEUJUH 10 I975 SHEET FIG.6

FIELD OF THE INVENTION This invention relates to a replaceable diggertooth for cutting and excavating hard, ice encrusted formations as wouldbe encountered in permanently frozen ground. The invention is alsouseful for excavating any hard, layered formation exhibiting aclotropicgrain characteristics such as sandstone and limestone. Theaforementioned formations can be failed by a scraping action as opposedto the harder isotropic granite and quartzite formations which are bestfailed by compressive force.

DESCRIPTION OF THE PRIOR ART Known digger teeth suffer primarily fromthe disadvantage that wear takes place rapidly, especially at thecorners of the teeth. As wear progresses, the tooth becomes less able topenetrate the terrain upon which they are working, leading to anincrease in the time used for excavating a given amount of material.

SUMMARY OF THE INVENTION The primary feature of this invention is theutilization of the undercutting principal at the tooth point. This toothundercuts a small portion of the formation on each side of the materialto be removed. The primary cutting portions of the tooth point precedethe excavating portion by a distance dependent upon the angle of attackof the tooth into the formation. More specifcally, according to theinvention a digger tooth comprises a mounting portion for attachment toan excavating machine, and a cutting portion formed by two curvedsurfaces as viewed in transverse cross-section, the surfaces forming theupper and lower tooth surfaces and varying in profile such that theouter longitudinal edges are thicker than the central portion. Thus, inuse, wear of the tooth takes place initially in the thinner centralportion so that the outer edges become the primary cutting portions.

By the above means, the life of the tooth is increased and therefore theefficiency of the machinery upon which such teeth are mounted is in turnincreased.

Further advantages and features will become apparent from the followingdescription of a preferred embodiment when read with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a tooth and holder mountedon the bucket lip of an excavating machine;

FIG. [A shows the relationship between the two curves on the forwardmostpoint of the cutting portion of the tooth;

FIG. 1B is a longitudinal section of the preferred tooth design takenalong line D-D of FIG. 1;

FIG. 2 is a vertical plan view of the tooth and holder shown in FIG. Iwhen the tooth is partially worn;

FIG. 3 is a side view, partially in section, of the worn tooth andholder shown in FIG. 2;

FIG. 4 is. a frontal view of the tooth and holder combination of FIGS. 2and 3 taken parallel to the formation being excavated.

FIGS. 5 and 5A show a comparison between the prefe rred tooth and aconventional tooth at the same angle of attack.

FIG. 6 shows a partial longitudinal section of the preferred cuttingstructure adapted to a different type of tooth and holder combination.

DETAILED DESCRIPTION Referring to FIG. 1, the plan view shows thereplaceable digger tooth I mounted in a holder 2 attached to a bucketlip 3. In the preferred embodiment the cutting edge 4 of the tooth l isformed, from the frontal view, of two circular arcs. The circular arcsare of different radius and are offset to one another such that thethickness of the cutting edge 4 increases from the center outwards. FIG.1A shows a frontal view of the cutting edge of FIG. 1 with the upperradius R and the lower cutting edge radius R optimized when R T and Ware set as defined below.

These equations generate the curved cutting edge profile in such afashion that the tooth section increases from a thickness T in thecenter to 4T on the outside edge of the cutting point or when X i W/ ,C4T.

FIG. 1B shows the dimension B as being constant over the majority of thecutting point length and T increasing at the rate of 2.5T per inch ofcutting point length. The blend-out radius R, is equal to or greaterthan R and is dependent upon actual tooth loading conditions. Protectionfor the leading edge of tooth holder 2 as shown in FIG. I is provided bythe blend out radius R, and the raised step 9 on the forwardmost portionof the shaft 10. Provision for retaining means is provided for by recess11 and a retainer as fully described in US. Pat. No. 3,665,623 grantedon May 30th, 1972 to Kenneth M. White or Canadian Pat. No. 890,315granted on Jan. 11th, 1972 to Kenneth M. White can be used.

FIG. 2 is a plan of the tooth and holder combination and illustrates theworn tooth profile 12 that the aforementioned cutting edge designgenerates. The leading edges 13 precede the tooth removal portion andunder cut the material to be removed. As the tooth proceeds into theformation the curved surface generated by R in FIG. 1A places a lateralshear load on the formation. The lateral shear load combined with thetensile load generated due to the angle of attack of the tooth on theformation causes formation failure.

As shown in FIG. 3, the angle of attack 15 determines the amount ofundercut 16. A quick and simple method of varying this angle isdescribed in Canadian Pat. No. 896,423 granted on Mar. 28th, 1972 toKenneth M. White. Increasing the angle of attack causes the undercutdistance 16 to decrease for soft formations such as clay. The cuttingedge on the tooth wears sharper and excavates more efficiently thanteeth not having the preferred cutting edge profile. Reducing the angleof attack causes the undercut distance to increase and the tooth loadingto change from shear to compressive. In permafrost formations, thetendency is for the teeth to slide on the ice. In this type of formationthe reduced angle of attack presents a long slender leading edge topenetrate the formation much the same as an ice pick. The cutting edgematerial on the tooth represented by 13 working under the material beingexcavated tends to hold the teeth in the formation. This overcomes amajor problem with conventional teeth which is rounding of the toothscutting edge so that the bucket wheel on rotary trenching machines inwhich the teeth are mounted slides on the formation rather than diggingin.

Maintaining B as shown in FIGS. 1A and 1B constant generates two raisedareas shown as flats 17 and 18 in H0. 4. Placing the raised areas alongthe outer edges of the tooths cutting surface causes the cutting edge towear straight as shown in FIG. 4 from the front view. in extremelyabrasive conditions there is a tendency for the profile to wear as shownby the phantom line 19. This leads to a compound shearing radius on thecutting edge and indicates the angle of attack should be reduced forthat particular formation. Maintaining a flat cutting profile withsquare corners is important in excavating hard layered formations sincethe sharp corner acts as a stress riser for shearing failure across theformation.

H68. 5 and 5A illustrate the comparison between the sliding surface onthe preferred cutting profile and a conventional tooth at the same angleof attack. The conventional tooth shown in FIG. 5A wears according tothe phantom line 20 and cuts a rounded bottom groove in the formationwhich leads to increased sliding and excavating time.

What l claim as my invention is:

l. A digger tooth for releasable attachment to an excavating machine,comprising a mounting portion and a cutting portion having a cuttingedge, said cutting portion having an upper concave and a lower convexsurface as viewed in transverse section, said surfaces varying inprofile such that the outer edges of the cutting portion are thickerthan its central part, whereby when said tooth is mounted and workingsaid outer edges undercut a portion of material on each side of thematerial to be removed.

2. A digger tooth according to claim 1, wherein said central part of thecutting portion gradually increases in thickness rearwardly from thecutting edge.

3. A digger tooth according to claim 2, wherein the increase inthickness rearwardly of the central part is at the rate of approximately2.5 times the thickness of the central part of the cutting edge per inchof cutting portion length as viewed in longitudinal section.

4. A digger tooth according to claim 1, wherein said outer edges of thecutting portion are substantially parallel.

5. A digger tooth according to claim I, wherein said upper concave andlower convex surfaces as viewed in transvere section are circular arcs.

6. A digger tooth according to claim 1 in which the profile forming theupper surface of the cutting portion is substantially constant over thelength of the cutting portion and the profile forming the lower surfaceof the cutting portion is moving relative to the upper surface such thatthe thickness of the central portion of a lateral section is increasingat a rate approximately 2.5 times the cutting portion terminal thicknessper inch of longitudinal cutting portion length as viewed inlongitudinal section, said thickness increasing from the terminus of thecutting portion towards the mounting means.

7. A digger tooth according to claim 1, wherein said thicker outer edgeshave narrow, flat, upper surfaces. l 1k

1. A digger tooth for releasable attachment to an excavating machine,comprising a mounting portion and a cutting portion having a cuttingedge, said cutting portion having an upper concave and a lower convexsurface as viewed in transverse section, said surfaces varying inprofile such that the outer edges of the cutting portion are thickerthan its central part, whereby when said tooth is mounted and workingsaid outer edges undercut a portion of material on each side of thematerial to be removed.
 2. A digger tooth according to claim 1, whereinsaid central part of the cutting portion gradually increases inthickness rearwardly from the cutting edge.
 3. A digger tooth accordingto claim 2, wherein the increase in thickness rearwardly of the centralpart is at the rate of approximately 2.5 times the thickness of thecentral part of the cutting edge per inch of cutting portion length asviewed in longitudinal section.
 4. A digger tooth according to claim 1,wherein said outer edges of the cutting portion are substantiallyparallel.
 5. A digger tooth according to claim 1, wherein said upperconcave and lower convex surfaces as viewed in transvere section arecircular arcs.
 6. A digger tooth according to claim 1 in which theprofile forming the upper surface of the cutting portion issubstantially constant over the length of the cutting portion and theprofile forming the lower surface of the cutting portion is movingrelative to the upper surface such that the thickness of the centralportion of a lateral section is increasing at a rate approximately 2.5times the cutting portion terminal thickness per inch of longitudinalcutting portion length as viewed in longitudinal section, said thicknessincreasing from the terminus of the cutting portion towards the mountingmeans.
 7. A digger tooth according to claim 1, wherein said thickerouter edges have narrow, flat, upper surfaces.